Traditional lighting systems typically rely on conventional lighting technologies, such as incandescent bulbs and fluorescent bulbs. But these light sources suffer from several drawbacks. For example, such light sources do not offer long life or high energy efficiency. Moreover, such light sources offer only a limited selection of colors, and the color of light output by these light sources generally changes over time as the bulbs age and begin to degrade. Consequently, light emitting diodes (LEDs) have become an attractive option for many applications. The vast majority of LED-based lighting systems, however, use fixed white LEDs with no tunable range.
Although LED-based systems are capable of having longer lives and offering high energy efficiency, several issues still exist including the degradation of color over time and the responsiveness of color tuning adjustments. These issues can be compounded when multiple LED-based lighting systems are placed near one another or are coupled directly to one another.
Moreover, printed circuit board assemblies (PCBAs) with LEDs often exhibit undesirable acoustic effects when the PCBAs are driven at particular (e.g., resonant) frequencies in the human hearing range (e.g., approximately 50 Hz to 25 kHz). For instance, sound may be produced by vibrating capacitors, such as piezoelectric ceramic capacitors that change dimensions in response to an applied voltage. Some inductors may also create noise by magnetostriction. Although solutions (e.g., specialty dampeners, low drive acoustic capacitors) have been proposed in an effort to reduce or eliminate these acoustic effects, this problem continues to plague PCBAs regardless of application (i.e., not just when used as part of a lighting system).
A light source can be characterized by its color temperature and by its color rendering index (CRI). The color temperature of a light source is the temperature at which the color of light emitted from a heated black body radiator is matched by the color of the light source. For a light source that does not substantially emulate a black body radiator, such as a fluorescent bulb or LED, the correlated color temperature (CCT) of the light source is the temperature at which the color of light emitted from a heated black body radiator is approximated by the color of the light source.
The CCT can also be used to represent chromaticity of white light sources. But because chromaticity is two-dimensional, Duv (as defined in ANSI C78.377) can be used to provide another dimension. When used with a MacAdam ellipse (which represents the colors distinguishable to the human eye), the CCT and Duv allow the visible color output by an LED-based lighting system to be more precisely controlled (e.g., by being tuned).
The CRI, meanwhile, is a rating system that measures the accuracy of how well a light source reproduces the color of an illuminated object in comparison to an ideal or natural light source. The CRI is determined based on an average of eight different colors (R1-R8). A ninth color (R9) is a fully saturated test color that is not used in calculating CRI, but can be used to more accurately mix and reproduce the other colors. The CCT and CRI of LEDs is typically difficult to tune and adjust. Further difficulty arises when trying to maintain an acceptable CRI while varying the CCT of an LED.
The figures depict various embodiments for the purposes of illustration only. While specific embodiments have been shown by way of example in the drawings and are described in detail below, the embodiments are amenable to various modifications and alternative forms. The intention is not to limit the disclosure to the particular embodiments described. Accordingly, the claimed subject matter is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.